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Axpert and Pylontech - premature "back to grid"


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My apologies if this has been asked before, but I have trawled through this forum and read a lot about the Axpert and Pylontech combo, and haven't been able to find a difinitive answer.  I'm hoping that someone can maybe throw some light on this funny problem?

I have a Mecer SOL-I-AX-5M (Axpert 5kva/4kw) - as it came out of the box a few years ago - no firmware mods/hacks etc.  The system has been running for years using a bank of lead-acid batteries, but the bank has deteriorated to the point where it needed replacement.  So it was "upgraded" to a Pylontech UP5000 battery.

Since there are warranty concerns when connecting these batteries to Axpert inverters, the installation parameters supplied by Pylontech were followed to the letter.  However, the system isn't behaving as I expect it to behave, and barely uses any battery before failing over to the grid after sunset.

The settings are as follows:

Program 01 = SbU
Program 02 = 50A
Program 05 = USE
Program 12 = 48V
Program 13 = 51V
Program 26 = 53.2V
Program 27 = 53.2V (not specified by Pylontech)
Program 29 = 47.5V

The behaviour is that the battery charges nicely during the day, and then starts feeding power back at night.  I expect that it should drain until the voltage drops under 48V, but it only runs down to 49.5V.  The moment it drops to 49.4V, it falls back to grid, only to go back to solar the next day again.  (The battery SOC leds still show between 4 and 5 lit at this stage, so there is still plenty of juice available, and I doubt if there was a chance that it could have dipped down to 48V because the power draw on the system is very linear.)

I've read a thread here that suggested setting Program 29 to always be 2V lower than program 12, but I haven't seen this mentioned anywhere else - and also does not compute with the settings supplied by Pylontech.  Could this be the reason for this? (And if so, is this a "bug" in older Axperts maybe fixed in newer models?)

The plan is to get ICC or Solar Assistant installed to monitor and control the inverter according to battery SOC, but if the basics aren't working, then I'm not sure that any of those will just magically "make this work".  Any suggestions would be very much appreciated!  Thank you!

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Hi sgs.

I have seen this a couple times and there are one or two things to keep in mind.

The UP5000 battery is designed to output around 2.5KW (50A discharge as indicated in manual). This can cause some confusion because a user will read 5KWh and assume that the battery can output 5000W. Once the load exceeds this value, it will cause a sharp voltage drop (even when it is only a momentary "spike").

So what tends to happen is that the inverter picks up this "voltage drop" and assumes that the battery has reached its "point back to grid" and then gets stuck waiting for the "point back to Battery" set point. Also note that when this happens, the battery voltage will pop back up as soon as the inverter transfers to grid (removes the load from the battery).

I understand that you mention that the load is linear so this should not be a problem but I figured it best to have this presented for clarity.

Having the back to grid voltage at 48V will leave your Lithium battery SOC rather high (probably around 75%). I have changed mine to a lower value to allow the inverter to make use of more of the stored power. See the image attached, it indicates that the battery can operate between voltages of 44.5V to 53.5V so allowing your inverter to draw from the battery to a voltage of 46.5V should not cause any issues. This does change the depth of discharge that your battery is operating under and would give you more usable wattage while the grid is available. 

Should this be the preferred solution, then it is important to note that you will also then have less reserved energy available should you experience a power outage at night time.

You are welcome to contact me directly for a more detailed look at you situation. https://mecadon.co.za/wp/

UP5000 Specs.PNG

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Thank you for the help - much appreciated!

I tried lowering setting 29 last night by 0.5 volts, and sure thing, the inverter kicked to grid at 49v this time, not at 49.5 as before.  So now will monitor SOC more closely and slowly lower the safe discharge voltage until a reasonable DOD is achieved.

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